Method of and apparatus for data communications between portable information terminals

ABSTRACT

Data communications are carried out between portable information terminals through infrared radiation with an energy source which may be either a battery in each of the portable information terminals or an external power supply therefor, at a data transmission rate which is relatively low when the portable information terminal is operated by the battery. If the power source is the incased battery, the data transmission rate is switched to a low rate, data to be transmitted are compressed, and the respective numbers of bits &#34;0&#34; and &#34;1&#34; contained in the compressed data are compared with each other. If the number of bits which require a greater amount of electric energy for transmission is greater than the other number of bits, then the value of bits is inverted. Data indicative of the low data transmission rate, the compression of the data, and whether the value of bits has been inverted or not are coded into header data which are added to the compressed data for transmission. The data transmission rate is adjusted, the compressed data are expanded, and the inverted value of bits is inverted back by a controller in response to the header data at the receiver side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of and an apparatus forcarrying out data communications between portable information terminals,and more particularly to a method of and an apparatus for carrying outdata communications between portable information terminals through awireless communication medium such as infrared radiation with an energysource which may either be a battery of limited capacity housed in eachof the portable information terminals or an external power supply ofunlimited capacity.

2. Description of the Related Art

One known portable information terminal, as disclosed in Japanese patentapplication laid-open No. 63-246048, which is used in a wireless signaltransmission system which employs a wireless signal such as a radiosignal for transmitting data between main and auxiliary units, transmitsdata at different transmission rates depending on the condition in whichthe wireless signal is propagated. Such a portable information terminalis usually powered by a battery, and communicates with another terminalthrough a wireless communication medium such as infrared radiation.Generally, the portable information terminal consumes a large amount ofelectric energy for wireless communications through infrared radiation,and the incased battery of the portable information terminal has alimited capacity because the portable information terminal is relativelysmall in size and light in weight. Consequently, the portableinformation terminal which effects wireless communications throughinfrared radiation cannot be used continuously for a long period of timedue to the limited battery capacity.

The wireless signal transmission system disclosed in the laid-open no.246048/1985 is capable of increasing the reliability of datatransmission by varying the data transmission rate according to thepropagation condition of the wireless signal. However, the disclosedwireless signal transmission system gives no solution to prevent thehigh consumption of the electric energy of the portable informationterminal without degrading the efficiency of the data transmission.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of and anapparatus for carrying out data communications between portableinformation terminals while minimizing the consumption amount ofelectric energy when the portable information terminal is in operationwithout degrading the efficiency of data transmission.

To achieve the above object, there is provided in accordance with thepresent invention a method of carrying out data communications betweenportable information terminals through infrared radiation with a powersource which may be either an incased battery of limited capacity eachof the portable information terminals or an external power supply ofunlimited capacity, at a data transmission rate which is relatively lowwhen the portable information terminal is operated by the battery,comprising the steps of compressing data to be transmitted from one ofthe portable information terminals to another portable informationterminal if the energy source is the battery, comparing the number ofbits "0" contained in the compressed data and the number of bits "1"contained in the compressed data with each other, inverting the value ofbits if the number of bits which require a greater amount of electricenergy to be consumed for transmission is greater than the other numberof bits, transmitting the compressed data together with at least one ofdata representing that the data have been compressed and whether thevalue of bits has been inverted or not, from the one of the portableinformation terminals to the other portable information terminal if theenergy source is the battery, and expanding the compressed data andinverting back the inverted value of bits in response to the data at thereceiver side information terminal.

The signal representing the modified content of data comprises codedheader data added to the compressed data, and receiver side portableinformation terminal decodes the coded header data.

According to the present invention, there is also provided an apparatusfor carrying out data communications between portable informationterminals through infrared radiation with an energy source which may beeither an incased battery of limited capacity housed in each of theportable information terminals or an external power supply of unlimitedcapacity therefor, at a data transmission rate which is relatively lowwhen the portable information terminal is operated by the incasedbattery, comprising a power supply detector for detecting whether theenergy source is the battery or the external power supply, means forcompressing data to be transmitted from one of the portable informationterminals to another portable information terminal if the energy sourceis the incased battery as detected by the power supply detector, meansfor comparing the number of bits "0" contained in the compressed dataand the number of bits "1" contained in the compressed data with eachother, means for inverting the value of bits if the number of bits whichrequire a greater amount of electric energy to be consumed fortransmission is greater than the other number of bits, means fortransmitting the compressed data together with coded header datarepresenting that the data have been compressed and whether the value ofbits has been inverted or not, from the one of the portable informationterminals to the receiver side portable information terminal if theenergy source is the incased battery, and means for decoding the headerdata, expanding the compressed data, and inverting back the invertedvalue of bits in response to the header head at the receiver sideportable information terminal.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings which illustrate an example ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a portable information terminal to which amethod of carrying out data communications between portable informationterminals according to the present invention is applied;

FIG. 2 is a detailed block diagram of a power supply detector, acontroller, and an infrared communication unit of the portableinformation terminal shown in FIG. 1;

FIG. 3 is a flowchart of an operation sequence of the portableinformation terminal for detecting the type of a power supply; and

FIG. 4 is a flowchart of an operation sequence of the portableinformation terminal for transmitting data when the portable informationterminal is powered by a battery.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a portable information terminal to which a method ofcarrying out data communications between portable information terminalsaccording to the present invention is applied, generally comprises apower supply detector 101 for detecting the type of a power supply whichsupplies electric energy to the portable information terminal, acontroller 102, an infrared (IR) communication unit 103 for transmittingdata to and receiving data from another portable information terminalthrough infrared radiation, a memory 104, a display controller 105, anda display unit 106.

FIG. 2 shows in detailed block form the power supply detector 101, thecontroller 102, and the infrared communication unit 103.

As shown in FIG. 2, the portable information terminal can be powered byeither a incased battery 201 or an AC power supply connected to an ACadapter 202.

The power supply detector 101 comprises a jack 203 to which the ACadapter 202 can be connected, and a sensor 206 in the controller 102.When an input current supplied to the jack 203 is detected by the sensor206, the sensor 206 sends a control signal 207 to a power supplyselector 204 which selects one of the electric energy supplied from thejack 203 and the electric energy supplied from the battery 201 forsupply to a power supply circuit 205.

The controller 102 has a compander 208 for compressing data to betransmitted and expanding data which have been received, using thememory 104.

The infrared communication unit 103 has an infrared communicationcontroller 209 for controlling the transmission of data to and thereception of data from another portable information terminal, aninfrared data transmitter 210 for transmitting data to another portableinformation terminal, and an infrared data receiver 211 for receivingdata from another portable information terminal.

The infrared data transmitter 210 has a light-emitting element such as alight-emitting diode (LED) or the like, and selectively turns on and offthe light-emitting element depending on bits of data to be transmittedfor thereby transmitting the data. For example, the infrared datatransmitter 210 turns on the light-emitting element for transmitting abit "1" of data, and turns off the light-emitting element fortransmitting a bit "0" of data.

The infrared data receiver 211 has a light-detecting element such as aphotodiode (PD) or the like, and receives infrared radiation transmittedfrom another portable information medium as data represented by a trainof bits "1" and "0" .

Operation of the portable information medium will be described below.

FIG. 3 shows an operation sequence of the portable information terminalfor detecting the type of a power supply.

The operation sequence of the portable information terminal fordetecting the type of a power supply will be described below withreference to FIGS. 1 through 3. The power supply detector 101 and thecontroller 102 monitors the jack 203 with the sensor 206 to detect thetype of a power supply connected to the portable information terminal.It is assumed that the portable information terminal is usually poweredby the battery 201, and is switched from the battery 201 to the AC powersupply when an input current supplied to the jack 203 is detected by thesensor 206.

When the portable information terminal starts to operate, the jack 203is monitored by the sensor 206. If no input current supplied to the jack203 is detected by the sensor 206 in a step 301 (FIG. 3), then it isdetermined that the portable information terminal is powered by thebattery 201 (YES in the step 301), the compander 208 of the controller102 is operated in a step 302, and the infrared communication controller209 is set to effect communications at a low rate in a step 303.

If an input current supplied to the jack 203 is detected by the sensor206 (NO in the step 301), then the compander 208 is not operated in astep 304, and the portable information terminal is switched from thebattery 201 to the AC power supply in a step 305. Thereafter, theinfrared communication controller 209 is set to effect communications ata high rate in a step 306.

After the portable information terminal has started to operate, the jack203 is also monitored by the sensor 206 to detect whether the portableinformation terminal is switched from the battery 201 to the AC powersupply or from the AC power supply to the battery 201. If power supplyswitching occurs, then the controller 102 controls the start and stop ofthe operation of compander 208, and setting of communication rate ofinfrared communication controller 209 in the manner described above.

FIG. 4 shows an operation sequence of the portable information terminalfor transmitting data when the portable information terminal is poweredby the battery 201.

The operation sequence of the portable information terminal fortransmitting data when the portable information terminal is powered bythe battery 201 will be described below with reference to FIGS. 1, 2,and 4.

The power supply detector 101 and the controller 102 monitors the jack203 with the sensor 206 to detect the type of a power supply connectedto the portable information terminal. If the portable informationterminal is energized by the battery 201, then data to be transmitted bythe infrared communication unit 103 are compressed by the compander 208in a step 401.

The compander 208 has therein a dictionary for compressing data, and thedata to be transmitted by the infrared communication unit 103 arecompressed using the dictionary in the compander 208.

More specifically, the compander 208 searches the dictionary for acharacter or a string of characters contained in the data. If thecompander 208 detects such a character or a string of characters in thedictionary, then the compander 208 compresses the data by replacing thecharacter or the string of characters with a number in the dictionary.If the compander 208 does not detect such a character or a string ofcharacters in the dictionary, then the compander 208 registers thecharacter or the string of characters in the dictionary.

The compander 208 registers strings of characters comprising previousand present agreed strings of characters in the dictionary. When thedictionary is full, the compander 208 discards a string of characterswhich has not been used for a long period of time. The compander 208manages the dictionary by managing each of strings of characters with aqueue, and placing a string of characters at the end of a queue eachtime a string of characters is used.

Then, the controller 102 calculates the entire length of bits of thecompressed data in a step 402, and then calculates the number of bits"1" in the compressed data in a step 403.

The controller 102 calculates the ratio of the bits "1" in thecompressed data to the entire length of bits of the compressed data, anddetermines whether or not the bits "1" in the compressed data is 50% ormore of the entire length of bits of the compressed data in a step 404.If the bits "1" in the compressed data is 50% or more of the entirelength of bits of the compressed data (YES in the step 404), then thecontroller 102 inverts the value of the bits of the compressed data,i.e., inverts the bits "1" in the compressed data into "bits "0", andthe bits "0" in the compressed data into "bits "1", thereby producingdata which will be transferred from the infrared communication unit 103in a step 405.

If the bits "1" in the compressed data is less than 50% of the entirelength of bits of the compressed data (NO in the step 404), then thecontroller 102 does not invert the value of the bits of compressed data.

Since the number of bits "0" in the compressed data is greater than thenumber of bits "1" in the compressed data, as a consequence, the entireperiod of time in which the light-emitting element of the infrared datatransmitter 210 is turned on is reduced, thus effectively reducing theelectric current consumed by the infrared data transmitter 210. If theinfrared data transmitter 210 is arranged such that the light-emittingelement emits light when the bits "0" are applied thereto, then thecontroller 102 inverts the value of the bits such that the number ofbits "1" in the compressed data is greater than the number of bits "0"in the compressed data.

To the data which have been compressed, there are added header datarepresenting that the data have been compressed and also representingwhether a bit inverting process has been carried out or not in a step406. The compressed data and the added header data make up data whichwill actually be transmitted from the infrared communication unit 103.

After the data have thus been processed for transmission from theinfrared communication unit 103, the data are transmitted from theinfrared data transmitter 210 to another portable information terminalunder the control of the infrared communication controller 209 in a step407.

If the portable information terminal is operated by the AC power supplyor another other external power supply, then the data to be transmittedare not compressed and inverted, and will be transmitted with headerdata representing that the data have not been compressed and a bitinverting process has not been carried out.

The other portable information terminal which has received thetransmitted data analyzes the added header data to determine whether thedata have been compressed or not and also a bit inverting process hasbeen carried out or not, and, if necessary, inverts again the value ofthe bits of the data to restore the original data and expand thecompressed data.

As described above, when the portable information terminal is powered bythe battery, since data to be transmitted are compressed and the datatransmission rate is switched to a low rate, the electric currentconsumed by the portable information terminal for wireless datatransmission through infrared radiation is reduced, and the period oftime in which the portable information terminal can continuously bepowered by the battery is extended.

Furthermore, inasmuch as data to be transmitted are compressed, they canbe transmitted with a relatively high data transfer efficiency even ifthe data transmission rate is switched to a low rate.

In addition, the value of bits in the compressed data are inverteddepending on the proportion of those bits, the electric current consumedby the portable information terminal for wireless data transmissionthrough infrared radiation is further reduced, and the period of time inwhich the portable information terminal can continuously be powered bythe battery is further extended.

It is to be understood that although the characteristics and advantagesof the present invention have been set forth in the foregoingdescription, the disclosure is illustrative only, and changes may bemade in the arrangement of the parts within the scope of the appendedclaims.

What is claimed is:
 1. A method of carrying out data communicationsbetween transmitting and receiving portable information terminalsthrough infrared radiation during which the transmitting terminal isoperated with power fed by an incased battery, at a relatively low datatransmission rate, the method comprising the steps of:(a) compressingdata to be transmitted at said transmitting portable informationterminal; (b) comparing the number of "0" bits contained in thecompressed data and the number of "1" bits contained in the compresseddata with each other; (c) inverting the value of bits if the number ofbits which require a greater amount of electric energy for transmissionis greater than the number of the other bits; (d) transmitting amodified content signal representing transmission data format,indicating that the transmission data is inverted if the bits have beenso inverted at step (c) and compressed, to the receiving portableinformation terminal; and (e) expanding the compressed data andinverting back the inverted value of bits in response to said signal atthe receiving portable information terminal.
 2. The method according toclaim 1, wherein said modified content signal representing thetransmission data format is coded into a header data added to saidcompressed data, and said receiving portable information terminaldecodes said coded header data.
 3. An apparatus for carrying out datacommunications between transmitting and receiving portable informationterminals through infrared radiation with an energy source which may beeither an incased battery of limited capacity in each of the portableinformation terminals or an external power supply of unlimited capacity,the data communications being at a data transmission rate which isrelatively low when the transmitting portable information terminal isoperated by the battery, the apparatus comprising:a power supplydetector for detecting whether the energy source is the incased batteryor the external power supply:means for compressing data to betransmitted when the transmitting portable information terminal detectsthat the energy source is the incased battery; means for comparing thenumber of "0" bits contained in the compressed data and the number of"1" bits contained in the compressed data with each other; means forinverting the value of bits if the number of bits which require agreater amount of electric energy for transmission is greater than theother number of bits; means for transmitting the compressed datatogether with coded header data representing that the data has beencompressed and whether the value of bits has been inverted or not whentransmitting the data when the power source is the incased battery; andmeans for decoding the header data, expanding the compressed data, andinverting back the inverted value of bits in response to said receivedheader data.